Method And Apparatus For Selecting Enhanced Dedicated Channel Transport Format Combination In Cell_Fach State And Idle Mode

ABSTRACT

A method and apparatus for selecting an enhanced dedicated channel (E-DCH) transport format combination (E-TFC) in Cell_FACH state and idle mode are disclosed. A wireless transmit/receive unit (WTRU) transmits a random access channel (RACH) preamble and receives an index to an E-DCH resource in response to the RACH preamble. The WTRU may estimate a power headroom based on the maximum WTRU transmit power, power offset value, and the last successfully transmitted RACH preamble transmit power. The WTRU restricts an E-TFC based on the estimated power headroom, and selects an E-TFC based on a set of supported E-TFCs. The WTRU then generates, and transmits, a protocol data unit (PDU) based on the selected E-TFC.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/408,128 filed Mar. 20, 2009; which claims the benefit of U.S.provisional application No. 61/038,176 filed Mar. 20, 2008, which isincorporated by reference as if fully set forth.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

It has recently been proposed, as part of third generation partnershipproject (3GPP) Release 8 work item applicable to high speed packetaccess (HSPA) systems, that wireless transmit/receive units (WTRUs) areallowed to transmit on an enhanced dedicated channel (E-DCH) in theCELL_FACH state or idle mode. The WTRUs are allowed to tap E-DCHresources without transitioning to CELL_DCH state, which is referred toas enhanced random access channel (E-RACH) access or E-DCH in CELL_FACHor idle mode.

An E-RACH access is a combination of a random access channel (RACH)preamble transmission phase and an E-DCH transmission phase. FIG. 1shows an E-RACH access procedure. The RACH preamble transmission phaseuses a subset of R99 RACH signatures that a Node B has designated orbroadcast for use in E-RACH. The reception of a preamble by the Node Bis acknowledged in an acquisition indication channel (AICH), which alsoassigns a WTRU with an index for a shared E-DCH resource to use. Theshared E-DCH resources are pre-designated by the Node B for use in anE-RACH access in CELL_FACH state or idle mode. For all shared E-DCHresources, the parameters are provided to the WTRU during initial setupor broadcast to WTRUs in the cell by the Node B. Each E-DCH resource isassociated with an index which is transmitted as part of theacknowledgement for the E-RACH access, or using some other signalingmechanism. Once the WTRU receives the index value, all configurationparameters related to the assigned shared E-DCH resource are known andthe WTRU may start transmitting after a possible synchronization period.

In E-DCH (Release 6 and above), the WTRU selects the number ofinformation bits to transmit at every transmission time interval (TTI)based on a set of pre-defined rules. Conceptually, this procedureincludes a number of steps. First, the WTRU determines the amount ofpower it can use for data transmission. To this end, the WTRU measuresits power headroom, which is defined as the ratio between the maximumtransmission power and the power of the dedicated physical controlchannel (DPCCH). The maximum transmission power is a known parameter atthe WTRU. It is either determined by the WTRU category or signaled bythe network. Thus, whenever the WTRU has an estimate of the DPCCH power,the WTRU can calculate the power headroom estimate. In this contextpower headroom estimation and DPCCH power estimation have a directrelationship. Since the DPCCH power is subjected to variations at everyradio slot in response to power control commands from the network, theWTRU filters the DPCCH slot-wise power estimates over a period of oneTTI, (i.e., 3 radio slots for 2 ms TTI and 15 radio slots for 10 msTTI). In a second step, the WTRU uses this power headroom to determinethe set of transport format that can be used for transmission, alsoreferred to as the set of supported E-DCH transport format combinations(E-TFCs). An E-TFC that is in the set of supported E-TFCs is said to bein supported state. This step may be referred to as E-TFC restriction.Finally, the WTRU determines how many bits will be transmitted in thecoming TTI from each MAC-d flows (up to the maximum supported E-TFC)based on the serving grant, non-scheduled grant, reference E-TFCs,hybrid automatic repeat request (HARQ) profiles, multiplexing list, etc.This step is referred to as E-TFC selection in the 3GPP specifications.

When the WTRU initiates E-DCH transmission in CELL_FACH state or idlemode, the WTRU may not know the power headroom or may not have asufficiently accurate power headroom estimate to carry out the E-TFCselection functions and protocol data unit (PDU) creation procedures intime for the start of the E-DCH dedicated physical data channel(E-DPDCH) transmission. Therefore, it would be desirable to provide amethod for power headroom estimation that would allow the WTRU toperform E-TFC selection functions and PDU creation procedures beforethat point. It is further desirable to provide such an estimation methodfor reporting UE transmission power headroom (UPH) measurements when thescheduling information (SI) containing the UPH is transmitted before themeasurement is considered sufficiently reliable.

SUMMARY

A method and apparatus for selecting an E-TFC in Cell_FACH state andidle mode are disclosed. A WTRU transmits an RACH preamble and receivesan index to an E-DCH resource in response to the RACH preamble. The WTRUmay estimate a power headroom based on the maximum WTRU transmit power,a power offset value, and the last transmitted RACH preamble transmitpower. The WTRU restricts an E-TFC based on the estimated powerheadroom, and selects an E-TFC based on a set of supported E-TFCs. TheWTRU then generates, and transmits, a protocol data unit (PDU) based onthe selected E-TFC.

Alternatively, the WTRU may estimate the power headroom based on thedownlink measurement and uplink noise and interference level. Thedownlink measurement may be common pilot channel (CPICH) received signalcode power (RSCP) measurement. Alternatively, the WTRU may select anE-TFC from a minimum E-TFC set within a default serving grant.Alternatively, the WTRU may select an E-TFC assuming that all E-TFCs areavailable for first N E-DCH transmissions independently of radioconditions.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 shows an E-RACH access procedure; and

FIG. 2 is a block diagram of an example WTRU in accordance with oneembodiment.

FIG. 3 is a block diagram of an example WTRU in accordance with oneembodiment.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “WTRU” includes but is notlimited to a user equipment (UE), a mobile station, a fixed or mobilesubscriber unit, a pager, a cellular telephone, a personal digitalassistant (PDA), a computer, or any other type of user device capable ofoperating in a wireless environment. When referred to hereafter, theterminology “base station” includes but is not limited to a Node-B, asite controller, an access point (AP), or any other type of interfacingdevice capable of operating in a wireless environment. Together, E-TFCrestriction and E-TFC selection are referred to as E-TFC selectionfunctions hereinafter.

Embodiments disclosed herein are related to power headroom estimationand to the selection of an E-TFC in the absence of the initial WTRUpower headroom information at the WTRU. The embodiments are applicableto 3GPP HSPA wireless communication systems and any other wirelesscommunication systems

In accordance with a first embodiment, a WTRU is configured to determinean estimate of the power headroom based on downlink measurements and anuplink interference level. The uplink interference level information maybe signaled from a Node B, or assumed by the WTRU. The WTRU maydetermine the estimate of the WTRU power headroom as follows:

Power_Headroom=Max_WTRU_Tx_Power+CPICH_RSCP−Uplink_Noise_plus_Interference+K;  Equation(1)

where Max_WTRU_Tx_Power is the maximum transmission power of the WTRU,CPICH_RSCP is the received signal code power (RSCP) of the common pilotchannel (CPICH) of the cell being accessed,Uplink_Noise_plus_Interference is the sum of thermal noise andinterference at the base station antenna, and K is a pre-determinedconstant whose value depends on factors that do not change significantlyin different situations, (e.g., required signal-to-interference ratio(SIR) of the DPCCH, margins, or the like). CPICH_RSCP may be filtered atLayer 3 to reduce variations due to fast fading.Uplink_Noise_plus_Interference value may be pre-determined based onconservative estimates of the maximum noise rise at the Node B, or maybe signaled by the Node B over system information.

Once the WTRU has determined the estimate of the power headroom, theWTRU may execute the E-TFC selection functions (including E-TFCrestriction and E-TFC selection) based on the power headroom estimateand optionally based on a default grant signaled over systeminformation. The E-TFC selected is then used for PDU creation andtransmission. Optionally, the first E-DCH transmission uses thisapproach for E-TFC selection and the following transmissions may use thenormal power headroom estimate for E-TFC selection functions.

The WTRU may estimate the power headroom in accordance with the firstembodiment either for the initial E-DCH transmission or for one orcombination of any of the following duration:

-   -   (1) The first N E-DCH transmissions;    -   (2) The first M transmission time intervals (TTIS) or any other        pre-determined time units, (e.g., radio slots, frames, etc.);    -   (3) The first KDPCCH slots or transmit power control (TPC)        commands that are sent to the Node B and/or received from the        Node B; and    -   (4) Until the first real power headroom determination, (i.e.,        the headroom is calculated from an actual DPCCH power        measurement), and E-TFC selection functions based on this power        headroom measurement have been completed. Once such an E-TFC has        been selected, the WTRU may resume normal E-TFC selection        functions.

In accordance with a second embodiment, the WIRU is configured toestimate the WIRU power headroom based on the transmission power usedfor the RACH preamble and is configured to perform E-TFC selectionfunctions using the estimated power headroom. FIG. 2 is a flow diagramof an example process 200 of estimating a power headroom and selectingan E-TFC in Cell FACH state and idle mode in accordance with the secondembodiment. A WTRU may receive a power offset value from a network (step202). The power offset value may be predetermined. The WIRU transmits aRACH preamble while implementing a power ramp-up (step 204). The WTRUestimates a power headroom based on a WTRU maximum transmit power, thepower offset value and a last transmitted RACH preamble transmit power(step 206).

The power headroom may be calculated as follows:

Power Headroom=Max_WTRU_Tx_Power−Preamble_Tx_Power−Offset;  Equation (2)

where Preamble_Tx_Power is the transmit power of the last successfullytransmitted RACH preamble, and Offset is a power offset that may bepre-determined or calculated based on a value signaled over systeminformation.

Once the WTRU has determined the estimate of the power headroom, theWTRU may execute the E-TFC selection functions (E-TFC restriction andE-TFC selection) based on the power headroom estimate and optionallybased on a default grant signaled over system information (step 208).The E-TFC selected is then used for PDU creation and transmission.Optionally, the first E-DCH transmission uses this approach for E-TFCselection and the following transmissions may use the normal powerheadroom estimate for E-TFC selection functions.

When the WTRU receives an ACK on AICH, the E-DCH resource is allocatedand the WTRU uses the power headroom estimated based on the transmissionpower of the corresponding RACH preamble for the E-TFC selectionfunctions. The E-TFC selected is then used for PDU creation for theinitial E-DCH transmission.

Alternatively, the WTRU may carry out power headroom estimation everytime a RACH preamble is transmitted during the power ramp-up. The WTRUthen uses the last value of the power headroom to carry out the E-TFCselection functions and create the PDU for the initial E-DCHtransmission.

Alternatively, the WTRU may carry out power headroom estimation andE-TFC restriction every time a RACH preamble is transmitted during thepower ramp-up. The WTRU then uses the last set of supported E-TFC tocarry out E-TFC selection and PDU creation for E-DCH transmission.

Alternatively, the WTRU may carry out power headroom estimation andE-TFC functions (including E-TFC restriction and E-TFC selection) everytime a RACH preamble is transmitted during the power ramp-up. The WTRUthen uses the E-TFC selected to create the PDU for E-DCH transmission.

Alternatively, the WTRU may carry out power headroom estimation, E-TFCfunctions (including E-TFC restriction and E-TFC selection) and PDUcreation every time a RACH preamble is transmitted during the powerramp-up. The WTRU then uses the last PDU created for the E-DCHtransmission.

The WTRU may estimate the power headroom in accordance with the secondembodiment either for the initial E-DCH transmission or for one orcombination of any of the following duration:

-   -   (1) The first N E-DCH transmissions;    -   (2) The first M transmission time intervals (TTIs) or any other        pre-determined time units, (e.g., radio slots, frames, etc.);    -   (3) The first K DPCCH slots or transmit power control (TPC)        commands that are sent to the Node B and/or received from the        Node B; and    -   (4) Until the first real power headroom determination, (e.g.,        after sending the DPCCH), and E-TFC selection has been        completed. Once an E-TFC has been correctly selected the WTRU        may continue with the selected E-TFC.

The WTRU may also use the power headroom estimated in accordance withthe first or second embodiment to report the UE power headroom (UPH) ifan SI is triggered while the actual power headroom is consideredunreliable, (e.g., for the first or first few E-DCH transmissions inCELL FACH, or for a predetermined duration).

In accordance with a third embodiment, a WTRU is configured to select anE-TFC from a minimum E-TFC set. The minimum E-TFC set is pre-configuredor signaled by a network. The WTRU selects an E-TFC from the minimumE-TFC set either for the initial E-DCH transmission or for one orcombination of any of the following duration, independently of the powerheadroom:

-   -   (1) The first N E-DCH transmissions;    -   (2) The first M TTIs or any other pre-determined time units,        (e.g., radio slots, frames, etc.);    -   (3) The first K DPCCH slots or TPC commands that are sent to the        Node B and/or received from the Node B; and    -   (4) Until the first real power headroom determination, (i.e.,        the headroom is calculated from an actual DPCCH power        measurement), and E-TFC selection functions based on this power        headroom measurement have been completed. Once such an E-TFC has        been selected, the WTRU may resume normal E-TFC selection        functions.

The minimum E-TFC set may be pre-determined or signaled over systeminformation. The WTRU may choose the minimum value from the minimumE-TFC set. Alternatively, the WTRU may choose a higher E-TFC value basedon a power headroom estimated in accordance with the embodimentsdescribed above and/or based on the amount of data the WTRU hasavailable for transmission. The value selected from the minimum E-TFCset should not correspond to a higher grant than the default grantprovided in the system information block (SIB).

A minimum E-TFC may be applied until the WTRU receives a new absolutegrant from the Node B over an E-D CH absolute grant channel (E-AGCH)that is associated with the E-DCH resource, or until the WTRU receives arelative grant over an E-DCH relative grant channel (E-RGCH) indicatingto increase its current serving grant. Alternatively, the minimum E-TFCmay be applied until collision resolution is resolved. For commoncontrol channel (CCCH) transmissions the minimum E-TFC may be appliedfor the duration of the transmission.

In accordance with a fourth embodiment, a WTRU is configured to assumethat the power headroom does not limit the E-TFC in its calculations forthe initial E-TFC selection (or N first E-TFC selections or N firstTTIs), independent of the actual radio conditions. In other words, theWTRU assumes that all E-TFCs within the limit of the default grant arein the supported state, (i.e., there is no E-TFC restriction per say),in the calculation of the E-TFC for the initial or N first E-TFCselections. The WTRU continues normal operation, (i.e., E-TFCrestriction is carried out so that not all possible E-TFCs are insupported state), as soon as a real determination of the power headroomis available.

The WTRU may select an E-TFC in accordance with the fourth embodimenteither for the initial E-D CH transmission or for one or combination ofany of the following duration:

-   -   (1) The first N E-DCH transmissions;    -   (2) The first M TTIs or any other pre-determined time units,        (e.g., radio slots, frames, etc.);    -   (3) The first K DPCCH slots or TPC commands that are sent to the        Node B and/or received from the Node B; and    -   (4) Until the first real power headroom determination, (i.e.,        the headroom is calculated from an actual DPCCH power        measurement), and E-TFC selection functions based on this power        headroom measurement have been completed. Once such an E-TFC has        been selected, the WTRU may resume normal E-TFC selection        functions.

FIG. 3 is a block diagram of an example WTRU 300 in accordance with oneembodiment. The WTRU 300 includes a transmit/receive unit 302, acontroller 304, and a measurement unit 306. The transmit/receive unit302 is configured to transmit a RACH preamble, receive an index to anE-DCH resource in response to the RACH preamble, and generate an E-DCHtransmission using the selected E-TFC. The controller 304 is configuredto select an E-TFC in accordance with any one of the embodimentsdisclosed above. The controller 304 may select the E-TFC based onestimated power headroom calculated based on a WTRU maximum transmitpower, downlink measurement generated by the measurement unit 306, andan uplink noise and interference level. Alternatively, the controller304 may select the E-TFC based on estimated power headroom calculatedbased on the WTRU maximum transmit power, a power offset value, and thelast transmitted RACH preamble power. Alternatively, the controller 304may select an E-TFC from a minimum E-TFC set within a default servinggrant. Alternatively, the controller 304 may select an E-TFC assumingthat all E-TFCs are available for first N E-DCH transmissionsindependently of radio conditions within a default grant.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

1. A method for performing enhanced dedicated channel (E-DCH) transportformat combination (E-TFC) restriction for E-DCH transmissions in CellForward Access Channel (Cell_FACH) state or idle mode, the methodcomprising: a WTRU transmitting a random access channel (RACH) preamble;the WTRU receiving an index to an E-DCH resource in response to the RACHpreamble; the WTRU estimating the power headroom for at least an initialE-TFC restriction based on at least a WTRU maximum transmit power, apower offset value and a last transmitted RACH preamble transmit power;and the WTRU performing E-TFC restriction to determine a set ofsupported E-TFCs based on the estimated power headroom.
 2. The method ofclaim 1 wherein the WTRU estimates the power headroom for apredetermined duration, following reception of the index.
 3. The methodof claim 1, wherein the WTRU bases the E-TFC restriction on theestimated power headroom for a duration of a variable number of firstdedicated physical control channel (DPCCH) slots or of a variable numberof first transmission time intervals (TTIs).
 4. The method of claim 3,wherein after the duration, the E-TFC restriction is calculated based ona DPCCH power measurement.
 5. The method of claim 1, wherein the WTRUreceives a power offset value via system information.
 6. The method ofclaim 1 further comprising: the WTRU selecting an E-TFC from the set ofsupported E-TFCs; the WTRU generating a protocol data unit (PDU) basedon the selected E-TFC; and the WTRU transmitting the PDU.
 7. The methodof claim 1 further comprising the WTRU sending scheduling informationincluding the estimated power headroom to a network.
 8. The method ofclaim 1 wherein the WTRU estimates the power headroom and performs E-TFCrestriction every time a RACH preamble is transmitted during powerramp-up.
 9. The method of claim 1 wherein the WTRU estimates the powerheadroom, performs E-TFC restriction, selects an E-TFC, and generates aPDU every time a RACH preamble is transmitted during power ramp-up. 10.The method of claim 1 wherein the WTRU performs the E-TFC restrictionbased on the estimated power headroom for a first E-DCH transmissionfollowing a RACH preamble transmission.
 11. A wireless transmit/receiveunit (WTRU) for performing (E-DCH) transport format combination (E-TFC)restriction for E-DCH transmissions in Cell Forward Access Channel(Cell_FACH) state or idle mode, the WTRU comprising: a transmit/receiveunit configured to transmit a random access channel (RACH) preamble,receive an index to an E-DCH resource in response to the RACH preamble;and a controller configured to estimate a power headroom for at least aninitial E-TFC restriction based on a WTRU maximum transmit power, apower offset value, and a last transmitted RACH preamble transmit power,and perform E-TFC restriction based on the estimated power headroom todetermine a set of supported E-TFCs
 12. The WTRU of claim 11 wherein thecontroller is configured to estimate the power headroom for apredetermined duration, following reception of the index.
 13. The WTRUof claim 11 wherein the controller is configured to base the E-TFCrestriction on the estimated power headroom for a duration of a variablenumber of first dedicated physical control channel (DPCCH)slots or of avariable number of first transmission time intervals (TTIs).
 14. TheWTRU of claim 13 wherein, after the duration, the controller isconfigured calculate the E-TFC restriction based on a DPCCH powermeasurement.
 15. The WTRU of claim 11 wherein the transmit/receive unitis configured to receives a power offset value via system information.16. The WTRU of claim 15 wherein the controller is configured to selectan E-TFC from the set of supported E-TFCs, generate a protocol data unit(PDU) based on the selected E-TFC, and transmit the PDU.
 17. The WTRU ofclaim 15 wherein the transmit/receive unit is configured to sendscheduling information including the estimated power headroom to anetwork.
 18. The WTRU of claim 15 wherein the controller is configuredto estimate the power headroom and perform E-TFC restriction every timea RACH preamble is transmitted during power ramp-up.
 19. The WTRU ofclaim 15 wherein the controller is configured to estimate the powerheadroom, performs E-TFC restriction, select an E-TFC, and generate aPDU every time a RACH preamble is transmitted during power ramp-up. 20.The WTRU of claim 15 wherein the controller is configured to perform theE-TFC restriction based on the estimated power headroom for a firstE-DCH transmission following a RACH preamble transmission.